Lesson plan
IC 438
IC 438 is a spiral galaxy in the constellation of Lepus. Its velocity with respect to the cosmic microwave background is , which corresponds to a Hubble distance of . However, 17 non-redshift measurements give a much closer distance of . It was discovered by American astronomer Lewis Swift on 7 January 1891. IC 438 is a Seyfert I Galaxy, i.e. it has a quasar-like nucleus with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, the host galaxy is clearly detectable.
Article summary
IC 438 is a spiral galaxy in the constellation of Lepus. Its velocity with respect to the cosmic microwave background is , which corresponds to a Hubble distance of . However, 17 non-redshift measurements give a much closer distance of . It was discovered by American astronomer Lewis Swift on 7 January 1891. IC 438 is a Seyfert I Galaxy, i.e. it has a quasar-like nucleus with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, the host galaxy is clearly detectable.
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
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